Brachytherapy is a method of delivering short range radiation, meaning radioactive pellets or “seeds” are implanted directly inside the cancerous tissue so that they will directly attack the cancer. This is the opposite of long range radiation, which is administered through a machine that delivers high-energy x-ray beams that are directed at the tumor from outside the body. The benefit of this form of radiation is that it allows the doctor to administer a higher dose of radiation in a shorter period of time.
When this procedure is used to treat other forms of cancer, it is done on an outpatient basis. However, when it is used in the treatment of mesothelioma, it is done intraoperatively, meaning as part of the operation that is performed to debulk or remove as much of the tumor as possible. Intraoperative Radiation Therapy (IORT) should not add to the overall operative time.
There are two methods of brachytherapy that are performed intraoperatively. The relatively newer procedure involves a measure of the chest cavity in which the tumor was not able to be removed with a minimum of one centimeter clear margin. In this instance, the radioactive iodine seeds are woven into a mesh-like fabric that is degradable. The mesh is stitched in a manner that creates a cover for the area that has the remaining mesothelioma. The radiation is delivered in doses spread out over three months, but the residual radioactivity can last up to a year.
The second, older procedure uses catheters positioned in the tumor. This is typically accomplished with the use of X-rays, ultrasound, CT scan, or MRI. At this time, the amount of time needed to deliver the proper dose of radiation is also calculated using a computer. Once the catheters are in place, they are then connected to a high dose radiation afterloader. This is a computerized machine into which the iridium pellets are inserted (afterloaded) once the doctor confirms that the catheters are in the proper positions to deliver the radiation dose effectively. The pellets are loaded individually and injected into each catheter. The dwell time or length of time each pellet remains in the catheter is digitally controlled, as is the dwell position, the location along the catheter that is selected for the release of the iridium. This process is repeated until the pre-determined level of radiation has been administered, at which time the catheters are removed and no radioactive seeds are left in the body.
Efficacy of Treatment
It is important to note that the efficacy of this treatment for mesothelioma is still being evaluated. Brigham and Women’s Hospital includes the following caveat its explanation of brachytherapy used to treat mesothelioma, “At present there are no prospective data to support this. A few centers are reviewing their clinical experience retrospectively. More data will be available within the following year.”
In a 2005 study conducted by researchers at the Department of Radiation Oncology, Memorial Sloan-Kettering Cancer Center (A pilot trial of high-dose-rate intraoperative radiation therapy for malignant pleural mesothelioma, PubMed), seven patients were given extrapleural pneumonectomy with intraoperative radiation therapy and six patients had pleurectomy with intraoperative radiation therapy between 1994 and 1996. The findings of the study showed that, “Serious complications requiring further intervention occurred in 3/6 (50%) of the EPP/IORT (extrapleural pneumonectomy/intraoperative radiation therapy) group and 1/5 (20%) of the PD/IORT (pleurectomy/ intraoperative radiation therapy) group.”